The Practical Zone System for Film and Digital Photography, 5th Edition

chapter four   

The Zone

As you have learned thus far, both film and digital photographers run into problems when they attempt to translate what they see into a final print that faithfully depicts that initial experience. If lighting and contrast conditions happen to be average, the final results may be adequate. But there are two persistent problems that routinely get in the way of successful photography:

First, if the contrast of what’s being photographed is too contrasty or too flat, the results are likely to be unsatisfactory.

Or, second, if what the photographer hopes to achieve is not a literal rendering of the subject but rather an interpretation ...